This invention relates in general to mass transfer and heat exchange columns and, more particularly, to a method and apparatus to improve vapor distribution in such columns.
Vapor and liquid interaction is required in many types of mass transfer and heat exchange processes. Typically, the vapor stream is introduced to a column below a region containing trays or a random or structured packing while the liquid stream is introduced into the column above the trays or packing. The vapor and liquid streams then flow in countercurrent relation through the region, with the tray or packing serving to distribute the downwardly flowing liquid stream over a larger surface area to enhance the interaction with the upwardly flowing vapor stream.
In order to increase the efficiency of the mass transfer or heat exchange taking place between the vapor and liquid streams, it is important that the vapor be uniformly distributed across the horizontal cross-section of the column, particularly at the lower vapor-liquid interface where the vapor enters the packing. When the vapor is introduced to the column below the packing, the velocity of the vapor can prevent the desired horizontal distribution of the vapor prior to its entry into the packing. In order to improve the vapor distribution, deflectors have been positioned in some columns in the flow path of the vapor to deflect the vapor in a plurality of directions. Another example of a conventional vapor distributor known as a vapor horn is disclosed in U.S. Pat. No. 5,106,544. The vapor horn disclosed in that patent comprises an annular housing which is open at the bottom and contains a plurality of vanes for causing downward deflection of the circumferentially flowing vapor stream. The downwardly deflected vapor is then said to rise in a uniform manner into a packing bed which is positioned radially inwardly from the vapor horn.
While circumferential vapor horns can function satisfactorily in many applications, it has been determined that a maldistribution of the vapor stream may result under certain operating conditions. This maldistribution is believed to be caused by the vapor stream traveling through a swirling or cyclonic flow path after it is discharged from the vapor horn. A low velocity zone is created in the center of the column and a high velocity zone is created adjacent the inner wall of the vapor horn as a result of this cyclonic vapor flow. These velocity differentials then reduce the amount of vapor entering the center portion of the overlying packing and increase the amount of vapor in the radial outer portions of the packing. Once the vapor has entered the packing, this maldistribution of vapor cannot be readily corrected and reduces the efficiency of the mass transfer occurring within the packing.
A need has arisen for an improved circumferential vapor distributor or horn which will overcome this cyclonic effect to provide a more uniform distribution of vapor across the horizontal cross-section of a mass transfer or heat exchange column.